About the Overall Railroad Rebuild Project

The UI Railroad Transmission Line Upgrade Project rebuilds UI’s transmission lines along the 25 miles of the Metro North Railroad(MNR) corridor between Fairfield and West Haven. This includes installation of approximately 500 new foundation supported galvanized transmission poles, upgrading of conductor size and installing sectionalizing switches at nearby substations. This project will enhance the structural integrity and reliability of the high voltage transmission lines along the MNR corridor allowing UI to continue to provide safe, reliable electric service to our customers for years to come.

Project Purpose and Need
Benefits to region and our customers

The upgrades will improve the reliability and resiliency of the transmission system, ensuring that the safe and reliable transmission of power is maintained throughout Fairfield and New Haven County in accordance with Federal reliability standards.

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Project Map

Project Scope

  • Staking, vegetation clearing, installation and removal of access roads and work pads
  • Installation of drilled foundations supporting monopoles and conductors
  • Installation of new sectionalizing switches at substations to increase reliability and operational flexibility
  • Removal of bonnet structures (top of poles which hold the power lines) on MNR Catenaries (cables which hold the lines)
  • Site Restoration


Construction start of first phase: Dec. 2017

Estimated in-service date of final phase: 2028 Q3


Construction Scope

Phase 1 - Baird Substation to Congress Substation

115kV Transmission Line Upgrade

  • Completed, in service 12/24/2018

Phase 2 - Housatonic River

Crossing Replacement

  • Completed, in service 6/7/2018

Phase 3 - HRX to Baird

Stratford 115-kV Transmission Line Upgrade Project consisting of the removal and relocation of northern and southern sections of existing 115-kilovolt (kV) transmission line structures from Connecticut Department of Transportation (ConnDOT) catenary structures within the Metro-North Railroad corridor to new 115-kV transmission line structures to be located within the existing ConnDOT right of way and upgrade of 115-kV conductors extending approximately 1.9 miles from UI’s Baird Substation to just west of the Housatonic River in Stratford, Connecticut, and related substation improvements

  • In construction: Nov 2019 to Aug 2021
  • Energized: February 2021

Phase 4 - Milvon to West River 115 kV Transmission Line Rebuild Project

Rebuild 9.5 miles from Milvon Substation (Milford, CT) to West River Substation (New Haven, CT).

Relocate the transmission lines off the existing CT DOT railroad catenary bonnets and install on independent monopoles with new insulators, hardware and conductor on new monopole structures in the railroad corridor.

  • Engineering August 2020 – Q3 2022
  • Construction Start Q4 2023
  • In-service   Q4 2028

Additional Links and Documents

More information is available in the Document Library

Phase 5 - Fairfield to Congress Substation

Rebuild 8 miles of overhead transmission lines from the Fairfield, CT border (UI/Eversource transition structure) to Congress Substation (Bridgeport, CT).

  • Relocate the circuit from Eversource/UI Transition structure (B648) to Structure B737, from the existing railroad catenary bonnets and install on new monopoles in the railroad corridor.
  • Relocate the overhead transmission lines from the existing railroad catenary bonnets and install on independent monopoles with new insulators, hardware and conductor from structure B737 to Congress Substation.
  • Detailed Engineering – Jan. 2022 to Q1 2024
  • Construction - Q2 2024 to Q2 2028.

Construction Process

UI is committed to working cooperatively with our customers, neighbors, community leaders and regulators as we improve reliability while minimizing disruption to the environment and community. We have a dedicated team of public outreach liaisons who will be involved throughout the duration of the project to answer any questions you may have.

Below are the stages of the project construction process that you may see in your community.


1) Laying matting and building access roads for construction vehicles while protecting the area

2) Tree clearing – trimming "danger trees" that may cause service interruption

3) Drilling foundations which will support the new galvanized steel poles

4) Setting the bolt cage for the foundation structure

5) Pouring concrete for the foundations

6) Final concrete cap for the steel monopoles

7) Setting the poles into the foundation

8) Stringing the wire (conductor) onto the poles

9) Restoration - grading, seeding & mulch. Access roads removed.

Updated May 2020

Milvon to West River Transmission Line Upgrade Project Video

Video transcript


UI is designing the Project to avoid and minimize negative impacts to the community and the environment. Early Project planning efforts included the completion of a set of resource assessments to clarify important planning considerations such as water resources; soil characteristics; cultural resources; and sensitive plant and animal species. Active regulatory coordination and reviews preceded numerous permitting efforts and are ongoing through the construction phase of the Project. UI has secured the necessary authorizations reviews and permits from agencies across federal, state and local administration agencies. Consultations and permits have been pursued from the following agencies for the Project:


  1. U.S. Army Corps of Engineers (USACE)
  2. U.S. Fish and Wildlife Service (USFWS)
  3. U.S. Environmental Protection Agency (EPA)
  4. Federal Aviation Administration (FAA)

State of Connecticut

  1. Connecticut Siting Council (CSC)
  2. Connecticut Department of Energy & Environmental Protection (CTDEEP)
  3. Connecticut State Historic Preservation Office (SHPO)

Local and Regional

  1. Towns of Fairfield, Bridgeport, Stratford, Milford, Orange, West Haven & New Haven

How the Electric Delivery System Works

The electric grid consists of high-voltage transmission lines and low-voltage distribution lines that transport electricity from power generation plants to community areas that need electricity.

United Illuminating (UI)

United Illuminating (UI) is a subsidiary of AVANGRID. Established in 1899, UI is engaged in the purchase, transmission, distribution and sale of electricity and related services to approximately 335,000 residential, commercial and industrial customers in the greater New Haven and Bridgeport areas of Connecticut. UI's service territory includes 17 Connecticut towns and cities in an area totaling 335 square miles along or near the shoreline of Long Island Sound.

For more information, visit uinet.com and avangrid.com

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